This paper contributes to the literature by identifying the casual effect of economic zones on firms' outward FDI. Using the data of Annual Survey of Industrial Firms (ASIF) merged with List of Chinese Firms' FDI, empirical results present the promoting effect of economic zones on firms' FDI and the mechanism of firms' productivity and financing constraints. After the robustness test, the results remain valid. Finally, this paper documents some heterogeneity of the effects across the types of economic zones, firms and FDI.